It is well known that the value of the current motor rotational torque is needed for many control and regulation functions. This current motor torque value is traditionally calculated in the motor control device on the basis of vehicle-specific as well as driving situation-specific values and is made available to other control devices through electronic interfaces (CAN-Bus). A transmission control device which triggers on the basis of stored control and/or regulation programs in an automatic transmission with which the activation of a shifting and starting clutch and/or final control elements in an automatic transmission to implement gear ratio change processes can be triggered also belongs to these control devices.
The motor torque value calculated by the motor control device, usually on the basis of the motor rotational speed, the fuel injection amount and other parameters, is at least too inexact for the control and regulation of an automatic transmission. Hence the calculated motor torque value can deviate more or less strongly from the actual motor torque value on the basis of influences, for example by a motor-side auxiliary unit drive, due to ventilator losses, due to dynamic effects, due to various loading pressures of the internal combustion machine and/or due to various ambient air pressure. Increases in torque belong to the dynamic effects if, for example, the motor rotational speed declines on the basis of an increased driving resistance and all rotating parts of the power train act to increase torque with their lagging rotating masses, or torque diminutions if while motor rotational speed is increasing, the inert rotating masses of the power train are first brought to that speed which the drive motor itself has in the sense of a hoisting effect.
A calculated motor torque value does not correspond to the torque incident upon the transmission input shaft due to the converter curve of the torque converter, especially in motor vehicles with an automatic transmission and a hydrodynamic torque converter connected downstream from this in terms of drive engineering. This has as a consequence that even the automatic gear reduction change procedures of the transmission cannot be so optimally conducted as when a measured torque value is available.
Moreover an interruption of fuel to the internal combustion machine can occur during the operation of a motor vehicle. To the extent that the motor torque is calculated, this malfunction has previously remained unconsidered in determining motor torque. The motor control device therefore gives the transmission control device as well as other motor vehicle control devices a falsely calculated motor torque value. If the motor vehicle now is driving on an incline, the transmission recognizes this incline because the motor vehicle becomes slower despite a specified high motor torque.
This situation is usually used by the transmission control device to introduce a downshift process so that a clutch is opened in this regard and the current gear is disengaged. A synchronization of the new speed by raising motor torque is, however, no longer possible due to the lack of fuel. The power train between the drive motor and the transmission is now open and the motor finally remains standing. A steering auxiliary pump driven by the drive motor in this way becomes functionless so that disadvantageously high steering forces are required of the driver.
Reference is made to German Patent 102 57 139 A1 in connection with the inexactitude of the calculated motor torque value mentioned. It is explained at the beginning in this publication that the transmission input torque, the value of the throttle valve opening on the internal combustion machine as well as the motor vehicle speed are frequently used as input magnitudes in connection with automatic transmissions in motor vehicles for controlling precise up and downshifting. Moreover the transmission input torque is estimated on the basis of the motor rotation speed especially with electronically controlled transmissions. These measurements are inexact so that usually torque sensors on the transmission shaft are used to record the transmission input torque precisely.
Moreover a regulating device for the bridging clutch of the converter of an automatic transmission is known from German Patent 195 13 695 A1. The clutch regulating device is outfitted with means for determining target slip values with which the slip rotational speed can be adjusted as a function of the rotational speed of the input element of the clutch, the motor torque and the accelerator activity in continuous slip operation of the bridging clutch to increase the lifetime of the bridging clutch and the converter as well as for diminishing the thermal output performance of the bridging clutch.
It is moreover provided with this regulating device that a torque sensor measures the torque incident upon the crankshaft of the motor vehicle drive motor or the pump side of the torque converter and not perhaps on the transmission input shaft, and makes it available to the regulating facility. It is moreover disclosed in this publication that an emergency type of operation is possible for the converter bridging clutch with the regulating facility. During this emergency type of operation, the target slip value is set to a minimal value if the converter oil temperature has exceeded an impermissibly high value due to a disturbance of the torque bridging clutch or the torque converter.